Network devices may include various interfaces that have different Maximum Transmission Units (MTUs). In this context, the MTU may represent and/or refer to the size of the largest packet capable of being transmitted via a certain interface. In some network paths, interfaces of one or more devices along the path may have different MTUs. For example, a source device at the beginning of a network path may have an MTU of 2000 bytes, while an intermediary device in the middle of the network path may have an MTU of 1400 bytes. Accordingly, the intermediary device may need to fragment packets of over 1400 bytes into segments of 1400 bytes or less before being able to forward the packets to the next downstream device in the path. When each fragmented segment of the packets reaches the destination device of the network path, the destination device may reassemble the segments to produce the original packets.
Unfortunately, the process of fragmenting and reassembling packets may be costly and/or time-intensive. For example, transmitting multiple packet segments may be less efficient than transmitting a single, larger packet. Moreover, some packets may be formatted or configured to prohibit and/or prevent fragmentation. For example, some packets may contain a flag or other notification that indicates, to devices within a network path, that the packets are to be dropped instead of fragmented upon reaching a device with an MTU smaller than the size of the packets. As a result, these packets may be unable to reach their intended destinations.
To avoid both fragmented and dropped packets, network devices and/or network administrators may implement a variety of techniques to determine a Path MTU (PMTU) of a network path. Packets sized to comply with or correspond to this value may be transmitted along the path without being dropped or fragmented. In one example, a traditional method for determining the PMTU of a network path may involve sending progressively smaller test packets along the path until a test packet successfully reaches the destination device of the path without being fragmented. While this process may be improved or optimized in various ways (e.g., by using a binary search or other algorithm to select test packet sizes), traditional methods for discovering PMTUs may generally require forwarding multiple test packets along a network path. Accordingly, these conventional methods may often delay or slow transmission of traffic along the path.
The instant disclosure, therefore, identifies and addresses a need for additional and improved apparatuses, systems, and methods for discovering PMTUs.